Research concerned magnesium (Mg) metabolism in the young infant and animal. Two hundred premature neonates with apnea and bradycardia, 93% of whom also had the respiratory distress syndrome, were studied retrospectively to learn whether Mg supplementation was beneficial. Group A = 61 infants who received 5 or more days of Mg Rx (11 plus or minus 1); Group B:5 with 3-4 dyas of Mg (3.6 plus or minus 0); and Group C:134 with 0-2 days of Mg (0.5 plus or minus .1). Compared with Group A, more Group C infants developed tachycardia (p less than 0.001), had apnea (p less than 0.001), bradycardia (p less than 0.001) and cardiorespiratory crises (p less than 0.001) over a longer period of time; had more prolonged chest retraction and postural drainage and more blood gas derangement. One C died following apnea. After going home, all A infants survived and none were readmitted for apnea; one B was readmitted for apnea and died; and 28 C infants were readmitted for apnea. There were four more C deaths, all diagnosed as the Sudden Infant Death syndrome. Prospective clinical trials of Mg supplementation are planned. Three studies in animal models are reported. 1) Renal calcinosis has been reported in furosemide-treated premature infants. Weanling rats were fed adequate or sub-optimal Mg. Furosemide aggravated the Mg deficiency syndrome and was associated with severely disordered Ca metabolism only in rats fed suboptimal Mg. Mg preserved Ca homostasis in furosemide-treated animals. 2) In studies of plasma catecholamines in weanling Mg deficient and Mg-fed rats, stimuli that had no effect on catecholamines in Mg-fed rats provoked precipitous increases in Mg deficient rats. Similar levels were found in Mg-fed rats only after inducing strychnine seizures. 3) Weanling rats were raised and studied aseptically to learn the effect of acute Mg deficiency on the lungs following the sudden seizure episode of that syndrome. Pulmonary findings included edema, hemorrhage and congestion. Mg-fed controls with strychnine-induced tetany had relatively mild changes.